STOP SMASHING THE PEDAL DOWN TO THE FLOOR!!!(Specifically AmysRam)
This also helps to reduce brake wear and will also save valuable rubber on your tire or tires, depending on whether open or locking diff.

On a more serious note, I found a bottle of GumOut entire fuel system cleaner helps.

Also pace yourself to red lights. See if you can time them just right to avoid gas and brake usage. It may seem difficult at first, but it helps with mpg and can be fun as you pass that idiot that raced past you earlier as he/she sits at the light(passing only happens on multi-lane, DO NOT TRY ON SINGLE LANE)

And check that air pressure ONCE a week!!!

These are a couple of things that people either forget to do or don't do at all!

I was getting 10 city/ 14-16 hwy when I was living up in the mountains.... where I believe our hills our the biggest!! lol jk... Anyway, Ive moved out to the plains and Im getting 13/18.... one other thing that really helps is keeping your air filter clean, and oil changed.... just regular maintenance with help keep your mileage high

Went from 13/13.5 to 18.5/19 mpg by changing to custom home made CAI!! Also use 45 lbs of air in front tires, YES, a LIL rough riding, but I can handle that. Use 40 lbs in rear tires. Don't know what in town driving is, I have a very Heavy rt. foot.